The present invention relates to an interactive communication system which transmits/receives data at a high speed using an existing communication system.
This application is based on Japanese Patent Application No.08-122057, filed May 16, 1996, the contents of which are incorporated herein by reference.
Recently, the internet (which uses a general analog telephone line) or a digital private line has become widely known as an interactive communication system. Using the internet, HTML (i.e., Hypertext Markup Language) formatted data (a document comprising an image, a sound and a character or text) can be browsed, and a number of large amount data which are stored in servers distributed all over the world can be received.
For interactive communication, there exists a usual television broadcast system for unidirectionally transmitting images and sound to a user over a plurality of channels. In a television broadcast, an empty portion of a television signal is used so that a character information (character broadcast) is transmitted by a plurality of channels. The television broadcast thus provides a communication system which can transmit a large amount of information to the user.
Furthermore, as an interactive communication system for transmitting/receiving more information between a plurality of users, there is such an interactive communication system as VOD (Video On Demand) using a private communication line network in which an up link/down link is provided in a CATV (cable television) system so that the interactive communication can be carried out.
In the case of accessing the internet using a fixed terminal, for example, a computer and the like provided at home or in an office, data can be transmitted at a high speed. However, in the case of using a portable type information terminal (a mobile terminal) carried by the user, since the data is transmitted via a relay station (a base station of the interactive communication network), a maximum data transfer rate is about 9.6 kbps. For example, the portable information terminal is used so as to access a WWW (World Wide Web) server on the internet and to browse HTML formatted data (i.e., documents comprising image, sound and character data). In this case, when the data of 150 kbytes is received, it takes about 15 seconds, and there is a problem in that the data transfer rate is too slow and is not practical.
In Europe, in a ground wave digital broadcast which is put to practical use as a television broadcast, a mobile communication which can realize a transfer rate of about 1 Mbps forms a part of the service. In the case of using this communication system, in the above example, the data can be received in about 2 seconds. However, in the television broadcast and the ground digital broadcast, even if the data can be transmitted at the high speed, the user can only receive the data. Thus, there is such a problem in that interactive communication cannot be carried out.
Furthermore, in such an interactive communication system as CATV using a private line, service cannot be provided to the user at an optional place (i.e., such as in a train, a hall or a conference center). In other words, CATV can be provided to the user only at a specific place. Thus, there is a problem in that thus service cannot be provided for a mobile type information terminal.